1. Field of the Invention
The invention relates to protective layers for optically readable data discs and, more specifically, to layers that confer resistance to ultraviolet radiation.
2. Description of Related Art
Optically readable data discs (such as CDs and DVDs) are exposed to many varied environmental conditions that can shorten their usable lifetime. Examples of these conditions include heat, cold, water, humidity, sunlight, and physical stress. These conditions can be routine or accidental. Accidental conditions can include spilled coffee, being left in a hot vehicle, bending, abrasion, and so on.
While many conditions have received attention in the industry, resistance to damage caused by light or ultraviolet radiation has not been well addressed.
Discs claiming ultraviolet resistance were released by the TDK Company in 2004 under the trade names ARMOR PLATED DVD™ (in US), SUPER HARD (in Asia), and SCRATCH PROOF (in Europe). The product was renamed DURABIS® in Jan., 2005. The discs are described as having three times greater resistance to UV light than other DVD media. The chemical content was not disclosed, but the UV resistance was contained in the substrate layer of the discs.
An inkjet protection spray is sold under the PRESSIT SPRAYFIX trade name (Medea International; Dundee, Scotland). The liquid material is sprayed from a can onto the surface of an inkjet printable disc, and is advertised to increase water resistance, reduce fading by providing UV protection, and protects the disc from scratches. The spray is applied onto the printed label, which is above the data layer on the polycarbonate substrate. A cross-section of the sprayed product would first intersect the sprayed material, the label, the data layer, and finally the polycarbonate disc substrate. The material that provides UV protection is not identified.
U.S. Patent Publication Nos. 2006-0210756 A1 (published Sep. 21, 2006) and 2001-0033915 A1 (published Oct. 25, 2001) offer a thin flexible polymer layer that is adhered to an optical storage disc using static cling. The polymer does not leave any residue on the disc, and is readily added or removed to a preformed disc. The polymer layer can contain an impregnated ultraviolet protection material.
U.S. Patent Publication No. 2003-0207120 A1 published Nov. 6, 2003) suggests use of clear hot stamp coating methods of creating durable protective coatings to the printed side of CDs. Heat and pressure are applied to a donor web containing carrier ribbon material to facilitate transfer of material to the surface of a digitally readable disc. The formed discs can have improved properties such as light fade resistance, ultraviolet light fade resistance, resistance to liquid penetration, resistance to vapor penetration, scratch resistance, and blocking resistance.
Exposure to ultraviolet light can damage dyes or other components of the data layer in discs. Despite the efforts made to date to improve the environmental resistance of optical media discs, resistance to ultraviolet radiation remains a poorly addressed issue. Thus, there exists a need for materials and methods to improve the ultraviolet radiation resistance of media.